Injury to the anterior cruciate ligament (ACL) is functionally disabling to an active individual, placing the knee at risk for additional injury. There is, however, little known about the best means of rehabilitating a patient who suffers an ACL disruption and undergoes an ACL reconstruction. Some conservative rehabilitation programs include activities that are designed to produce low strains across the ACL graft, while other, more aggressive programs are aimed at rapid rehabilitation and are thought to produce greater strain magnitudes on the graft. The object of this study is to compare aggressive and non-aggressive rehabilitation programs over time in a prospective randomized trial, and to determine which is optimal. Comparison of the two rehabilitation programs will be made through measurements of the biomechanical behavior of the knee with the stressradiograph analysis technique, while the biochemical markers of articular cartilage matrix metabolism and degradation will be evaluated.